1. Field of the Invention
The present invention relates to electron flash units used with cameras and other imaging devices. More particularly, the present invention relates to systems and methods used to regulate the amount of light emitted by such flash units.
2. Description of the Related Art
Electronic flash units for use with cameras and imaging devices are well known, Also well known, are systems and methods for controlling and regulating the amount of light that is emitted by such electronic flash units. For example, two popular systems and corresponding methods for controlling and regulating light emission are known as the "automatic light regulating method" and the "flashmatic method."
In the case of the automatic light regulating method, light emission of an electronic flash device is stopped at a point in time during imaging operations when an amount of light reflected by a subject/scene to be imaged/photographed has reached a threshold amount (as realized by a sensor within a flash unit, in a camera, etc.). Because the amount of reflected light usually is predictable, it is possible to perform flash photography, for example, based on a standardized amount of flash illumination. As such, the automatic light regulating method has made it is so possible to emit an amount of flash illumination independently of subject range, camera settings such as aperture value, etc.
In the case of the flashmatic method, the amount of light emitted by an electronic flash device is adjusted based on the calculation of a "guide number." Such a guide number, in turn, may be used to control the start and stop times associated with flash illumination during an imaging operation. For example, the following equation has been used to calculate guide numbers (GN) for use in flash illumination regulation and control: EQU GN=R.times.F (3)
In equation (3), R is the photographic range such as the illumination range from an electronic flash device to a subject/scene to be imaged. F is the aperture value of a camera, for example.
As such, using a standard guide number GN.sub.Sv5 at a film sensitivity Sv5 (ISO 100 equivalent, etc.), equation (3) is as follows: EQU GN.sub.Sv5 =R.times.F.times.2.sup.(SV5)/2 (4)
Accordingly, a subject at a distance or a range R can be illuminated with the appropriate amount of illuminating light by adjusting the flash time of an electronic flash device to correspond to guide number GN as found from evaluation of equations (3) and (4).
With the flashmatic method as described above, the amount of illuminating light emitted by an electronic flash device is controlled and regulated without the effects of subject/scene reflectivity, etc. Accordingly, a relatively bright subject or a relatively dark subject usually can be photographed/imaged without realizing "gray" images.
Unfortunately, the aforementioned methods for regulating flash illumination have shortcomings which have not heretofore been adequately addressed by prior regulation systems. For example, the automatic light regulating method often results in images that are gray in appearance, especially when used to regulate light emission relative to scenes that either are very bright (e.g., scenes where reflection is high) or very dark (e.g., scenes where reflection is low), Accordingly, if a relatively large amount of light is reflected back to a camera, for example, flash illumination may be terminated too early thus resulting in a relatively dark image or photograph. Conversely, if a relatively low amount of light is reflected bask to a camera, for example, flash illumination may be terminated too late thus resulting in over-illuminated and exposed images.
In the case of the flashmatic method of flash illumination regulation, it too has problems which are not adequately addressed and which cause the generation of improperly illuminated scenes and subjects and, ultimately, improperly exposed images. That is, because the amount of illuminating light is determined based on calculating a guide number, the method is subject to erroneous measurements, calculations (e.g., rounding errors), etc. For example, range detection can be improperly measured and/or calculated, thus resulting in early or late termination of flash illumination, etc.
In order to improve on the shortcomings of the two regulation methods described above, others have proposed light regulating methods which incorporate both of the aforementioned methods into a single apparatus, Such an apparatus is proposed in Japanese Laid-Open Patent Publication No. Hei 9-105976. Unfortunately, with such a combined approach, a light source such as a flash tube may be prevented from illuminating light upon realization of an upper limit point in time or a lower limit point in time. Effective utilization of the automatic regulation technique is not achieved.
As such, the decision of camera and imaging device designers to implement one method over another to regulate flash unit output has, at best, been one that is imprecise. To combat such problems, designers have sought to refine the methods independently of each other without squarely addressing flash unit illumination output. As such, users of cameras and other imaging devices continue to run the risk of losing valuable images due to imprecise flash unit output regulation.
Thus, there exists a need to solve the aforementioned problems associated with the flash unit illumination regulation systems and methods described above. To solve such problems, new and improved systems and methods must be provided which take advantage of the benefits of such prior systems and methods and which avoid the above-stated shortcomings. To be viable such new and improved systems and methods must be able to combine both the automatic regulation and the flashmatic methods of flash unit light emission regulation into a single device that can automatically determine which method to use based subject parameters to produce the best images and photographs that are possible.